Next-Generation Multifunction Power ICs Help Shrink Mobile Systems

Nov. 5, 2007
To meet size constraints, a single IC functions as a power subsystem-on-a-chip by integrating combinations of linear and switching power sources, battery chargers, and even audio amplfiers.

With mobile equipment manufacturers demanding ever smaller and lighter handheld systems, the trend is to create smaller ICs that offer greater functionality. However, meeting those functionality, size, and weight requirements becomes a more difficult proposition in power-oriented applications.

For instance, switching regulators must be very efficient, particularly when multiple switchers are integrated into an IC. Battery- charger circuits must be efficient. Also, chip layout must ensure that there are no "hot spots" and electromagnetic interference (EMI) is controlled. On top of that, many handhelds operate from a single lithiumion/ polymer cell. Despite these difficult design issues, many IC manufacturers have responded with devices that meet the system requirements.

Take Linear Technology's LTC3555, the first in a family of multifunction power-management solutions for Li-ion/polymer battery applications. It integrates a switching PowerPath manager, a standalone battery charger, an ideal diode, I2C control, three high-efficiency synchronous buck regulators, and an always-on low-dropout regulator (LDO) (Fig. 1).

The LTC3555's PowerPath control seamlessly manages power flow between an ac wall adapter or USB port, Li-ion battery, and system load while its "instant-ON" operation ensures system load power even with a dead or missing battery. For fast charging, the LTC3555's switching input stage converts nearly all of the 2.5 W available from the USB port to charging current.

This enables up to 700 mA from a 500-mA limited USB supply and up to 1.5 A when wall-powered. An internal 180-mV ideal diode plus optional external ideal diode controller provide a low-loss power path, further minimizing heat generation and maximizing efficiency.

The LTC3555's three integrated synchronous buck regulators feature 100% duty-cycle operation and can deliver 1-A/400-mA/400-mA outputs, respectively, with adjustable output voltages down to 0.8 V. The internal low-RDS(ON) switches deliver efficiency as high as 94%, maximizing battery run time.

In addition, Burst Mode operation optimizes efficiency at light loads with a quiescent current of 35 mA per regulator (<1 mA in shutdown). The 2.25-MHz switching frequency allows use of tiny low-cost capacitors and inductors less than 1 mm in height. Furthermore, the regulators are stable with ceramic output capacitors, achieving very low output voltage ripple.

The LTC3555 features USB-compatible programmable current limiting to 100 mA/500 mA/1 A, while its Bat-Track adaptive output control enables high-efficiency charging and reduces power dissipation. Standalone autonomous operation simplifies design, eliminating the need for an external microprocessor for charge termination. To preserve battery energy, the LTC3555 draws <23 mA from the battery in suspend mode. The charger is compatible with inputs up to 5.5 V (7-V absolute maximum transient for added robustness).

The powerwise interface National Semiconductor's LP5552 is a PowerWise Interface (PWI) 2.0-compliant energy management unit (EMU) for applications such as baseband processors in mobile phones and other portable equipment (Fig. 2). It operates cooperatively with processors using an advanced power controller (APC) to provide adaptive voltage scaling (AVS), which significantly improves processor efficiencies over conventional powerdelivery methods.

The LP5552 is intended for use in a voltage scaling system that lowers the system's power dissipation. Scaling supply voltage with the clock frequency of a processor is a huge power saver. Also, the device supports two types of voltage scaling - dynamic voltage scaling (DVS) and AVS.

DVS systems switch between pre-characterized voltages, which are paired to clock frequencies used for frequency scaling in the processor. AVS systems track the processor performance and optimize the supply voltage to the required performance. AVS is a closed-loop system that provides process and temperature compensation to deliver the minimum supply voltage for any given processor, temperature, or clock frequency.

To support DVS and AVS, the LP5552 is programmable via the low-power, two-wire PWI. This serial interface controls the various voltages and states of all regulators in the LP5552. Both slaves in the LP5552 support the full PWI command set, other than the optional extended register read and write, as described in the PWI 2.0 specification: core voltage adjust, reset, sleep, shutdown, wakeup, register read, register write, and authenticate.

The PowerWise technology is an advanced energy-management solution for energy-constrained digital devices, like mobile phones, PDAs, handheld gaming consoles, and personal navigators. Developed by National Semiconductor in collaboration with ARM, it enables longer battery life, more features, and improved user experience by reducing the energy consumption in digital processors by up to 70%.

Operating from a 2.7- to 4.8-V input, it's compatible with single-cell Li-ion batteries. The LP5552 contains two 88% efficiency, switching dc-dc buck converters that are programmable from 0.6- to 1.235-V outputs. Switching frequency is 3.6 MHz, and output current measures 800 mA per switcher. They supply two voltage scaling domains, and five digitally programmable LDOs are available for supplying additional support circuitry.

Three digital output pins can be used as you see fit. By default, they're configured as open-drain outputs, outputting a logic "0." In the open-drain configuration, they can be referenced to any voltage less than the VDD of the LP5552. The three output pins are guaranteed to sink and source 1 mA.

Charge management Texas Instruments' TPS65820 is a fully integrated solution for handheld devices, integrating charge management, multiple regulated power supplies, system management, and display functions in a small, thermally enhanced 7- by 7-mm package. The high level of integration enables typical board area space savings of 70% compared to equivalent discrete solutions, while implementing a high-performance and flexible solution.

If required, an external host may control the TPS65820 via an I2C interface, with access to all integrated subsystems. The I2C allows for the setting of output voltages, current thresholds, and operation modes. Internal registers possess a complete set of status information, enabling easy diagnostics and host-controlled handling of fault conditions. The TPS65820 can operate in standalone mode, with no external host control, if the internal power-up defaults are compatible with the system requirements.

The TPS65820 contains a complete charge-management solution for single Li-ion/Li-pol cells with thermal foldback, dynamic power management, and pack temperature sensing, supporting up to 1.5-A max charge current. Programmable charge parameters provide for an ac adapter and USB port operation

The device integrates nine LDOs: six adjustable-output LDOs (1.25 to 3.3 V); two fixed-voltage LDOs (3.3 V); one fixed-voltage, always-on LDO (3.3 V); and one real-time-clock (RTC) backup supply with low leakage (3.1 V). Also, there are two 600-mA output current, 0.6- to 3.4-V programmable dc-dc buck converters with enable, standby mode operation, and an automatic low-power mode setting.

Two open-drain, pulse-width-modulation (PWM) outputs allow for programmable frequency and duty cycle control. They can be used to control keyboard backlight, vibrator, or other external peripheral functions. An RGB LED driver with programmable flashing period has individual R/G/B brightness control. A constant-current white LED driver, with programmable current level, brightness control, and overvoltage protection, can drive up to six LEDs in series configuration.

Among its features are dual-input power-path functionality with input current limiting and overvoltage protection. An integrated power-on-reset function with programmable masking monitors all supply outputs. It comes with software and hardware reset functions, too. An eight-channel integrated analog-to-digital converter (ADC) samples system parameters with single conversion, peak detection, or averaging operating modes.

In operation, the host can set system parameters and access system status using an I2C interface. There's an interrupt function with programmable masking that signals system status modification to the host. Three generalpurpose I/O (GPIO) ports are programmable as drivers, integrated analog-todigital triggers, or buck converters with standby-mode control.

Dual buck converters Many applications only require a pair of dcdc converters and LDOs. Maxim's MAX8667 and MAX8668 four-channel power-management ICs (PMICs) come in a 9-mm2 thin quad flat no-lead (TQFN) package (Fig. 3). They minimize total solution size by integrating two step-down dc-dc converters and two low-input LDOs, as well as all feedback networks.

To further save space and cost, they utilize a 1.5-MHz switching frequency to enable the use of tiny external components, such as 0805 2.2-μH inductors. The MAX8667 and MAX8668 are well-suited for cell phones, PDAs, and other space-constrained, handheld applications.

In addition to saving space, the MAX8667 and MAX8668 extend battery life. They do so by integrating a synchronous rectifier in each dc-dc converter to achieve up to 93% efficiency while drawing only 100-μA (typ) quiescent current with all regulators enabled.

One of the dc-dc converters delivers up to 1.2-A output, while the other delivers up to 600 mA. The low-input LDOs operate down to 1.7-V input, saving 80% of total power loss in the system compared to conventional linear- regulator solutions.

The output voltages of the dc-dc converters are adjustable from 0.6 to 3.3 V (MAX8668) or factory preset (MAX8667). The output voltages of the low-noise LDOs are all factory preset to eliminate the need for an external feedback network.

The MAX8667 and MAX8668 stepdown regulators are optimized for high-efficiency voltage conversion over a wide load range while maintaining good transient response, minimizing external component size, and minimizing output voltage ripple. Packaged in a 3- by 3-mm TQFN, these PMICs are fully specified for the extended temperature range of -40°C to 85°C.

Programmable power manager The SMB113A/B and SMB117 power-management ICs from Summit Microelectronics include all of the essential blocks for implementing a complete four-channel power subsystem consisting of four synchronous stepdown buck controllers (Fig. 4). Digital programmability lets designers customize the devices to suit many multichannel power-supply applications. Complete with a GUI, all programmable settings, including output voltages and I/O voltage monitoring, are customizable.

These ICs integrate four PWM controllers and a wide range of sophisticated power-management functions that eliminate the need for many external components, which ultimately reduces system cost and space. They offer four identical channels of PWM dc-dc stepdown (buck) converters. PWM channels are digitally programmable for output characteristics and monitoring, including voltage output levels to ±1.5% accuracy.

The SMB113A switches at 800 kHz, while the SMB117 switches at 400 kHz and the SMB113B operates at 1 MHz. Switching dead-time is adjustable and can be programmed at the factory for optimized performance. Furthermore, the IC's high drive capability allows a delivery of 10 A or higher, using a wide variety of industry-standard MOSFETs.

Complementing the precise power regulation are advanced power control features, which include static and dynamic output voltage scaling and margining, independent channel sequencing/enable, and output slew rate control. The devices additionally provide complete power system diagnostics, including input and output monitoring for undervoltage/overvoltage (UV/OV) conditions. A built-in reset monitor eliminates the need for external reset ICs.

With an input range of 2.7 to 6.0 V, the SMB113A/B and SMB117 suit a wide range of mobile applications. The devices come in both the commercial and industrial operating temperature ranges. Packaging is lead-free, RoHScompliant (Restrictions on Hazardous Substances), 5- by 5-mm QFN-32 (quad flat no-lead).

Power-management unit The AS3603 from Austriamicrosystems is a highly integrated, CMOS powermanagement device. It's designed specifically for portable devices such as mobile phones, PDAs, CD players, digital cameras, and other devices powered by one-cell lithium-based or three- to four-cell nickel-based batteries. The IC incorporates LDOs, dc-dc converters, a complete battery charger, and an audio power amplifier on one die.

Ten linear LDOs feature 30-μVRMS noise from 100 Hz to 100 kHz. Line and load regulation is <1 mV static and <10 mV transient. Power-supply rejection ratio (PSRR) is >70 dB at 1 kHz. Two digital low-power LDOs output 0.75 to 2.5 V, 200 mA; three RF lownoise LDOs output 1.85 to 3.4 V, 150 mA; two RF low-noise LDOs output 1.85 to 3.4 V, 150 mA; one SIM lowpower LDO produces 3.0 V, 20 mA; one periphery low-noise LDO yields 2.5 to 3.2 V, 150 mA; and one low-power LDO produces 2.5 V, 10 mA.

The integrated, programmable stepdown dc-dc converter doesn't require an external Schottky diode yet provides up to 95% efficiency throughout the whole operating range. It provides 1.0 to 3.0 V, up to 500 mA.

The step-down converter can be used as a standalone device or as a pre-regulator for LDOs to increase overall device efficiency. A 15-V, 45-mA stepup converter supplies power for white LEDs together with programmable current sources to control LED brightness.

A low-distortion audio power amplifier (1 W at 8 Ω) supports handsfree mobile-phone operation and HiFi ringtones. It provides 0.5 W at 4 V for stereo and 1 W at 8 Ω when bridged. A digital volume control produces 3-dB steps.

The device also features a chemistryindependent battery charger that includes fuel gauge circuitry, automatic trickle charging, programmable constant current, constant voltage, and pulse charging. It offers automatic trickle charging, programmable constant current charging, programmable constant voltage charging, programmable pulse charging, safety functions (low battery shutdown), operation without battery, and no-battery detection. The charger operates with a wide battery supply range of 3.0 to 5.5 V

The AS3603 is controlled via a serial interface and integrates all necessary system-specific functions, such as reset, watchdog, and power-on detection. Its regulator output voltages are programmable by software. Also, eight preset startup timings can be selected by an external resistor.

Other features on the device include four general-purpose switches (1 and 2 Ω), on-chip bandgap tuning for high accuracy (±1%), integrated programmable watchdog (7.5 to 1900 ms), programmable reset (10 to 110 ms), typical shutdown current of 7 μA (2.5 V always on), and overcurrent and thermal protection. The AS3603 employs a 0.35-μm CMOS in a 48-pin, 6- by 6-mm QFN package (0.4-mm pitch) or a 48-pin, 7- by 7-mm QFN package (0.5-mm pitch). Power dissipation is 2.1 W at TAMBIENT = 70°C.

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